Multitrial inhibitory avoidance learning in the crab Chasmagnathus.

Chasmagnathus crabs placed in the dark compartment (DC) of a double-chamber device and given electrical shocks whenever they entered or remained in the light compartment (LC), showed an LC-avoidance behavior when tested 24 h after a training session of three 30-min periods with 60-min intervals. The avoidance behavior depended neither on the shock number nor on the distribution at training but only on exposure to the LC-shock contingency, thus suggesting that crabs learn to associate the LC with an aversive situation. The learning outcome disclosed a higher degree of refraining from entering the LC rather than a faster escaping to the DC. Distributed practice proved more effective on crab avoidance learning than massive practice. Retention of the learned behavior occurred after a 24-h rest interval in an environment different from that of the training apparatus. Experimental devices previously used in avoidance learning studies with crabs were improved here by automating both the computation of latency values and the event recording.